An image processing apparatus selectively sets a feature of securing the confidentiality of real data indicated by allocation data by an enabler attached to the apparatus when the real data left in a storage device are no longer necessary. The image processing apparatus (100) stores in a memory (11) an erasing program for erasing used data in an HDD (19). After executing an image forming process using the data in the HDD 19, if it is detected that an enabler (1) is inserted into an USB interface 20 to lift the restriction on the use of the erasing program, a CPU (10) deletes the allocation data for the unnecessary data and starts the erasing program to overwrite/erase the corresponding real data to secure the confidentiality of the real data. If otherwise, the CPU (10) does not overwrite/erase the real data.